PORTLAND, ME - April 4: Joshua Nisbet, 36, of Scarborough, faces up to 30 years in prison and has been ordered by a judge to go to trial later this month in Portland without an attorney to represent him. Photographed during an interview at the Cumberland County Jail Friday, April 4, 2014. (Photo by Shawn Patrick Ouellette/Portland Press Herald via Getty Images)

PORTLAND, ME - April 4: Joshua Nisbet, 36, of Scarborough, faces up to 30 years in prison and has been ordered by a judge to go to trial later this month in Portland without an attorney to represent him. Photographed during an interview at the Cumberland County Jail Friday, April 4, 2014. (Photo by Shawn Patrick Ouellette/Portland Press Herald via Getty Images)

PORTLAND, Maine (AP) -- A robbery defendant is standing trial without a defense lawyer after a judge stripped him of the right to counsel, saying he was abusive toward his five previous court-appointed lawyers.

Joshua Nisbet, who maintains his innocence, gave a brief statement at the start of his trial Monday and frequently leaned over to consult a stand-by attorney as he questioned witnesses. He addressed the witnesses while seated behind a table with a fabric skirt to prevent jurors from seeing that he was wearing shackles.

A judge had stripped Nisbet of his right to a lawyer after he went through five court-appointed attorneys, all of whom asked to be taken off the case. The last two attorneys withdrew after Nisbet allegedly threatened to shoot one of them in the eye with a BB gun. Nisbet denied the accusation.

"It's a strange situation for everyone to be in," said Luke Rioux, one of two attorneys appointed by the judge to advise, but not represent, Nisbet.

Nisbet, 36, of Scarborough, has been in Cumberland County Jail for nearly three years since he was charged with wielding a knife during a convenience store robbery in South Portland in July 2011.

The Portland Press Herald reported that Nisbet may be the first criminal defendant in Maine forced to represent himself after being stripped of his constitutional right to an attorney.

Rioux and fellow stand-by attorney Mark Peltier said they were aware of no similar case in Maine in which a defendant who qualified for a court-appointed attorney was not allowed to have one. Justice Thomas Warren ruled that Nisbet effectively forfeited the right to a lawyer through his actions.

"I am representing myself (over) my objection, and I am only doing this under duress in this crazy situation," Nisbet told the judge before the jurors arrived.

On Monday, convenience store cashier Diane Angers described how a man wearing a ski mask and wielding a knife approached her from behind and demanded a bag of money. She said she thought the man was joking at first.

"When I turned around, this gentleman had a knife in his hand," said Angers, who wiped her eyes as she described the encounter.

Nisbet claims he's the victim of a police conspiracy that includes forged documents.

The robbery trial will last several days in Cumberland County.

"He's not an attorney. He's never been trained in the law, but he's doing the best he can," Peltier said.